224 SOILS AMD SUBSOILS OF SYDNEY AND SUBURBS. 



The drift sand beds occur over one extensive area to the south 

 and south-east of the city and lie partly on the sandstones and 

 partly on the clay shales. The sandstone bounds the sand beds on 

 the east, the clay shales bound them on the west. There are 

 numerous sandhills and ridges on the area, several of which attain 

 a fair elevation. The greater portion of the surface however is 

 fairly uniform, rising gradually from Botany Bay on the south 

 towards the city on the north. The surface formation having 

 been developed chiefly by seolian action, basins are numerous, and 

 as they have no outlet on the surface, in rainy seasons become 

 charged with water which gradually soaks away. The sand beds 

 are charged with water, the level of which varies with the rainfall. 

 They gradually thin out where they overlie the clay shales and as 

 the surface of the shale beds inclines towards the south, the water 

 which descends through the sand meeting the impervious shale is 

 deflected in that direction. It is almost a certainty that no water 

 is stagnant in the sandy substrata, but that there is a continual, 

 although slow movement towards Botany Bay. In some level 

 places, notably about Redfern, Waterloo, and Alexandria the 

 motion of the subterranean water is probably so slight as to 

 virtually render it equivalent to stagnation. On some of the low 

 lying portions of the sand beds there are considerable accumulations 

 of peaty material. 



Along the shores of the Parramatta River, chiefly at the outlets 

 of its numerous tributaries and at the heads of shallow bays, and 

 also at the embouchure of Cook's River, mud flats occur, some of 

 these are of considerable extent. They are all of them but slightly 

 elevated above the tide level and are always in a wet condition. 

 The mud consisting largely of washings from the land contains a 

 high percentage of organic matter. 



The foregoing descriptions of the four divisions of soils on the 

 metropolitan area enable them to be classified according to their 

 relative healthiness. 



The soil of the sandstone areas is well drained and there are 

 few natural organic impurities in it, therefore that area may be 

 considered healthy. 



The clay shale areas have a soil containing organic matter 

 overlying a clayey subsoil, which is always in a moist or wet 

 condition. The clay shale areas must necessarily be classed as 

 relatively unhealthy ; but not all over in the same degree. That 

 is to say, the summits and upper portions of the slopes are probably 

 very little inferior to porous and well drained summit sandstone 

 strata. The lower portions of the slopes and the valley bottoms 

 which have not elevation to facilitate drainage are undoubtedly 

 unhealthy. The fogs and mists which form on them after sun 



